Free hydroxylamine, NH_{2}OH, has been isolated by M. Lobry de Bruyn,
and a preliminary account of its mode of preparation and properties is
published by him in the current number of the _Recueil des travaux
chimiques des Pays-Bas_ (1891, 10, 101). The manner in which the free
base was obtained was briefly as follows. About a hundred grammes of
hydroxylamine hydrochloride, NH_{2}OH.HCl, were dissolved in six
hundred cubic centimeters of warm methyl alcohol. To this solution a
quantity of sodium dissolved in methyl alcohol was added, in such
proportion that the hydrochloride of hydroxylamine was present in
slight excess over and above that required to convert it to sodium
chloride. After deposition of the separated sodium chloride the
solution was decanted and filtered.
The greater portion of the methyl alcohol was next removed by
distillation under the reduced pressure of 160-200 mm. The remainder
was then treated with anhydrous ether, in order to completely
precipitate the last traces of dissolved sodium chloride. The liquid
eventually separated into two layers, an upper ethereal layer
containing about 5 per cent. of hydroxylamine, and a lower layer
containing over 50 per cent. of hydroxylamine, the remainder of the
methyl alcohol, and a little dissolved salt. By subjecting this lower
layer to fractional distillation under 60 mm. pressure, it was
separated into three fractions, of which the first contained 27 per
cent. of hydroxylamine, the second 60 per cent., and the third
crystallized in the ice-cooled receiver in long needles. This third
fraction consisted of free solid NH_{2}OH. Hydroxylamine as thus
isolated in the free state is a very hygroscopic substance, which
rapidly liquefies when exposed to air, owing to the absorption of
water.
The crystals melt at 33°, and the fused substance appears to possess
the capability of readily dissolving metallic salts. Sodium chloride
is very largely soluble in the liquid; powdered niter melts at once in
contact with it, and the two liquids then mix. Free hydroxylamine is
without odor. It is heavier than water. When rapidly heated upon
platinum foil it suddenly decomposes in a most violent manner, with
production of a large sheet of bright yellow flame. It is only very
slightly soluble in liquid carbon compounds, such as chloroform,
benzene, ether, acetic ether, and carbon bisulphide. The vapor attacks
corks, so that the solid requires to be preserved in glass-stoppered
bottles. The free base appears also to act upon cellulose, for, upon
placing a few drops of the melted substance upon filter paper, a
considerable amount of heat is evolved. The pure crystals are very
stable, the base in the free state appearing to possess much greater
stability than when dissolved in water. The instability of the
solution appears, however, to be influenced to a considerable extent
by the alkalinity of the glass of the containing vessel, for
concentrated solutions free from dissolved alkali are found to be
perfectly stable. Bromine and iodine react in a remarkable manner with
free hydroxylamine.
Crystals of iodine dissolve instantly in contact with it, with
evolution of a gas and considerable rise of temperature. Bromine
reacts with violence, a gas again being explosively evolved and
hydrobromic acid formed. The nature of the gas evolved is now
undergoing investigation. A letter from M. Lobry de Bruyn appears in
the number of the _Chemiker Zeitung_ for October 31, warning those who
may attempt to prepare free hydroxylamine by the above method that it
is a dangerously explosive substance when warmed to a temperature of
80°-100°. Upon warming a flask containing the free solid base upon a
water bath a most violent explosion occurs. A spontaneous
decomposition appears to set in about 80°, and even in open vessels
the explosion is very violent. Care must also be taken during the
fractional distillation of the concentrated solution in methyl alcohol
to cool the apparatus before changing the receiver, as if air is
admitted while the retort is heated the experiment ends with an
explosion.--_Nature_.
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